1. Field of Invention
This invention relates to a water-dilutable preservative concentrate and to an emulsion prepared therefrom for preserving fabric, wood, timber, leather, and various films generated from polymer latices.
2. Description of the Prior Art
Preservatives are often used in conjunction with the manufacture of fabrics, wood products, leather, and other substrates subject to microbial attack. Attack by fungi and bacteria can lead to discoloration and/or degradation of the substrate. Often the preservative is applied by dilution into water and subsequent dipping of the article to which the preservative is applied. In addition, the preservative can be prediluted in water or added directly to a liquid matrix to preserve subsequent films formed upon drying of the matrix, i.e., polymer emulsions or paints.
If the preservative is water insoluble it is often combined with water immiscible solvents and emulsifiers so that on addition to water an emulsion forms in which the preservative is, at least initially, uniformly dispersed in the aqueous medium. It is known to incorporate such preservatives, e.g., isothiazolones with fungicidal properties such as those marketed by Rohm and Haas Company as Kathon biocides, into the treatment mixture.
A problem which has been noted in applications which involve dipping a substrate, such as fabric, wood, leather, and the like, into emulsions of isothiazolone fungicides, is that the isothiazolone may be taken up by the substrate in a non-uniform manner due to poor homogeneity of the emulsion. Related problems occur where emulsions are used to impregnate wood. This is accomplished by introducing the isothiazolone emulsion into a vessel containing the wood to be impregnated, and applying pressure and vacuum according to various defined procedures. The emulsion not taken up by the wood is pumped into a storage tank where is remains, with little or no agitation, until reused to impregnate subsequent batches. Often the stored emulsion must remain unagitated during non-use periods, or overnight, weekends, etc. Emulsions which are prepared and held unagitated, before addition to polymer laticies or paints have the same homogeneity problems. The problem is especially acute in situations where the emulsion is prepared and used over a period of weeks with little or no agitation. Separation of emulsions can lead to overdosing or underdosing the preservative.
One approach to solving the problem of inhomogeneity caused by separation of the oil phase with time is to formulate a microemulsion, such as described in U.S. Pat. No. 4,954,338. The small particle size (&lt;1000 A) of the microemulsion precludes phase separation but typically requires five to ten times the amount of emulsifier needed to form macroemulsions. It has been observed that high emulsifier levels can sometimes be detrimental to retention of isothiazolone on the preserved substrate when the substrate (fabric, wood, leather, and the like) subsequently comes into contact with water during use or storage. High levels of emulsifier can solubilize water insoluble preservative resulting in loss of a portion of the isothiazolone and a lesser degree of preservation than expected from a given concentration of isothiazolone. The degree of solubilization is dependent upon the amount of emulsifier present. It is usually desirable to minimize the amount of emulsifier present as regards the loss of preservation on subsequent exposure to water.
It is known to use a mixture of isothiazolones, emulsifiers, and organic solvents to prepare emulsive concentrates of isothiazolones for dilution into aqueous systems. However, these emulsive concentrates do not possess good "phase stability" (lack of phase separation) upon being diluted; one factor contributing to the tendency of these mixtures to undergo phase separation is the large density differential that exists between the isothiazolone/solvent phase and the aqueous phase.
It is known to use a mixture of agricultural pesticides/insecticides/herbicides, emulsifier, and organic solvents for dispersal and/or dilution into aqueous solutions for applications to crops, plants, soil, and the like. Commercially used pesticide emulsive concentrates are usually considered satisfactory and adequate if they do not phase separate within one to two hours after dilution, because agitation is usually present during application.
In the case where solvents alone are used to dissolve the isothiazolone preservative, known as the "isothiazolone concentrate", the concentrate is diluted on site into the aqueous treatment solution for dipping of a substrate or impregnation of wood. Solvents used to make up conventional isothiazolone concentrates are typically of the low density (specific gravity &lt;0.9), aromatic hydrocarbon type, e.g., xylene. These solvents possess the necessary solubility characteristics to dissolve significant amounts of water-insoluble isothiazolones such as 4,5-dichloro-2-n-octyl-3-isothiazolone. These particular isothiazolone concentrates also contain a small amount of emulsifier in order to produce a dispersion/emulsion once the concentrate is diluted into the aqueous solution to be used to treat the wood. Due to the large density differential between the solvent concentrate and the aqueous solution in which the concentrate is being diluted, the resultant emulsion of isothiazolone very often is unstable in terms of homogeneity, i.e., phase separation occurs between the bulk aqueous phase (specific gravity of approximately 1.00 for water) and the solvent-isothiazolone phase (specific gravity of approximately 0.95). This tendency to phase separate causes problems in repeated use of the aqueous emulsions to treat substrates with isothiazolone preservatives in that within a short time the uptake of isothiazolone into the substrate becomes non-uniform due to non-homogeneous exposure to the isothiazolone. The dip tank method of treating substrates such as fabric, wood, leather, and the like, requires a significant degree of solution/emulsion homogeneity for an extended period of time in order to treat with a precise amount of preservative. Other situations where emulsions of isothiazolones are prepared, used intermittently, and stored without agitation, such as preemulsification before adding to latex, or impregnation of wood, have similar homogeneity requirements.